Accompanying recent popularization of computers, an inkjet printer is widely used for printing letters or an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of jetting out a liquid droplet by applying a pressure from a piezoelectric element, a system of jetting out a liquid droplet by generating a bubble in the ink under heat, a system of using an ultrasonic wave, and a system of jetting out a liquid droplet by suction using an electrostatic force. The ink composition used for such inkjet recording includes an aqueous ink, an oily ink and a solid (fusion-type) ink. Among these inks, an aqueous ink is predominating in view of production, handleability, odor, safety and the like.
The coloring agent used in such an inkjet recording ink is required to have high solubility in a solvent, enable high-density recording, provide good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing to an image-receiving material and less bleeding, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost. However, it is very difficult to find out a coloring agent satisfying these requirements in a high level. Various dyes and pigments for inkjet recording have been already proposed and are actually used, but a coloring agent satisfying all of the requirements is not yet found out at present. Conventionally well-known dyes and pigments having a color index (C.I.) number can hardly satisfy both color hue and fastness required of the inkjet recording ink. Heretofore, studies are being made on a dye having fastness and good color hue with an attempt to develop a dye excellent as the dye for inkjet recording.
However, in the compound as a water-soluble dye, a water-soluble group is necessarily substituted. If the number of water-soluble groups is increased so as to improve the stability of ink, this has been found to cause a problem that the formed image is readily blurred under high-humidity conditions.
An object of the present invention is to provide an inkjet recording ink composition and an inkjet recording method, which cause less blurring of image under high-humidity conditions.